1. Field of the Invention
The present invention relates to a camera for use with a film having a magnetic memory portion. More specifically, the present invention pertains to an improvement in a magnetic head of such a camera, for writing or reading to or from the magnetic memory portion of the film.
2. Description of the Related Art
U.S. Pat. No. 4,977,419 discloses a type of photographic film (simply referred to as "film" below) having a transparent magnetic layer on the side of the film base, and discloses a type of camera having a magnetic head for writing or reading information to or from the aforementioned magnetic layer of the film.
The '419 patent also discloses a plurality of recording tracks for magnetically recording that are provided outside a photographic frame of the film. This is because it is intended that increasing the number of the recording tracks increases an amount of information that can be recorded for each frame.
The kinds of information recordable by the camera, include a date and a time of a photographing operation, the kind of illuminating light source at the time of the photographing operation, pseudo-zoom information and photographic information pertaining to a shutter time, an aperture value, etc.
U.S. Pat. No. 4,878,075 discloses a type of film wherein film information pertaining to the film speed, the specified number of photographic frames, etc. is previously-recorded, and also discloses a type of camera which reads this information from the film before a photographing operation and rewrites this information during a film winding operation after the photographing operation, to record various kinds of photographic information at the time of the photographing operation on the film.
The '075 patent discloses that the camera writes "exposed information" indicating an exposure operation has been completed, to every photographic frame which has been exposed, as a part of the photographing information. (The term "exposed information" pertains to information relating to the exposure of a previously exposed photographic frame.) Moreover, the '075 patent discloses that the film is rewound halfway through use and removed from the camera. When the rewound film is reloaded into the same camera or loaded into another camera, a magnetic head of the camera detects whether there is the exposed information with respect to each photographic frame of the film, and enables an exposure operation to automatically resume from an unexposed frame of the film. (This is referred to as "auto-set function at the time of reloading the film.") That is, this is realized by means of the camera reading the photographic information, which the same camera or another has written, from the rewound film when the film is reloaded into the same camera or loaded into a different camera.
Now, in order to read the film information previously-recorded on the magnetic layer on the side of the film base, or in order to write the photographic information to the magnetic layer of the film in response to the photographing operation by means of the magnetic head, which is arranged in the camera, it is necessary to transport the film in a state where the magnetic head (especially a track forming portion thereof) is in close contact with the aforementioned magnetic layer of the film. For this reason, the camera is usually arranged in such a manner that the film is held under a urging force between the magnetic head positioned on the side of the base of the film and a pad positioned at a location to face the magnetic head on the emulsion layer side of the film. As a result, the film suffers scrapes and pressure marks caused by the pressure of holding the film between the magnetic head and the pad. Therefore, the camera should read the film information from and should write the photographic information to an area of the film excluding the photographic frame.
On the other hand, the magnetic layer may be provided on the side of the film base, all over the film base, as disclosed in the '419 patent. For this reason, in order to prevent the image quality of a photograph from deteriorating owing to the presence of the magnetic layer, the number of magnetic particles, i.e., the density, provided for the magnetic layer is limited to be a very small number. Therefore, a signal output obtained when the camera reads the film information is very small. Moreover, the camera has an electromagnetic noise source, such as a film transporting motor, near the magnetic head, so that a S/N at the time of reading the film information is not satisfactorily obtained in cooperation with the aforementioned very small signal output.
The signal output V from the magnetic head has the following relationship: EQU V.alpha.Tw.times.T.times.S.
Wherein, Tw is a width of the track forming portion of the magnetic head in the perpendicular direction to the film transporting direction, i.e. the core width of the magnetic head; T is the number of coil turns around the core of the magnetic head; S is a film transporting speed.
In order to enlarge the signal output V, it is necessary to enlarge the width of the track Tw, to increase the number of coil turns T, or to increase the film transporting speed S.
However, it is difficult to increase the film transporting speed owing to the size of a battery loadable in the camera, that is, owing to the limited electric power available for a film transporting operation.
Increasing the number of coil turns T enlarges the size of the magnetic head, which results in enlarges the size of the camera.
Broadening the width of the track Tw causes the following problem.
It is desirable that a reading track for reading the film information from the film also may be used for the writing to (recording on) the film, whereby the number of the recording tracks is increased, and the photographic information recordable for one film frame is increased. That is, after reading the film information from a track where the information is previously-recorded (when the film information is read from the track, this track is referred to as a "reading track"), it is desirable that to write new information over the previously-recorded information in order to also reuse the reading track as a "recording track", to increase the amount of information for one film frame.
As above-described, the '419 patent discloses increasing the number of the recording tracks in order to increase the amount of the recordable information. However, if the width of the track Tw is broadened, the number of the recording tracks cannot be increased. Therefore, the amount of the recordable information cannot be increased.